Ultraviolet radiation induces both full activation of ret kinase and malignant melanocytic tumor promotion in RFP-RET-transgenic mice.
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Biomedical subjects
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BACKGROUND: The calcimimetic agent R-568 lowers plasma parathyroid hormone (PTH) levels in hemodialysis patients with mild secondary hyperparathyroidism, but its efficacy in those with more severe secondary hyperparathyroidism has not been studied. METHODS: Twenty-one patients undergoing hemodialysis three times per week with plasma PTH levels between 300 and 1200 pg/mL were randomly assigned to 15 days of treatment with either 100 mg of R-568 (N = 16) or placebo (N = 5). Plasma PTH and blood ionized calcium levels were measured at intervals of up to 24 hours after oral doses on days 1, 2, 3, 5, 8, 11, 12, and 15. RESULTS: Pretreatment PTH levels were 599 +/- 105 (mean +/- SE) and 600 +/- 90 pg/mL in subjects given R-568 or placebo, respectively, and values on the first day of treatment did not change in those given placebo. In contrast, PTH levels fell by 66 +/- 5%, 78 +/- 3%, and 70 +/- 3% at one, two, and four hours, respectively, after initial doses of R-568, remaining below pretreatment values for 24 hours. Blood ionized calcium levels also decreased after the first dose of R-568 but did not change in patients given placebo. Despite lower ionized calcium concentrations on both the second and third days of treatment, predose PTH levels were 422 +/- 70 and 443 +/- 105 pg/mL, respectively, in patients given R-568, and values fell each day by more than 50% two hours after drug administration. Predose PTH levels declined progressively over the first nine days of treatment with R-568 and remained below pretreatment levels for the duration of study. Serum total and blood ionized calcium concentrations decreased from pretreatment levels in patients given R-568, whereas values were unchanged in those given placebo. Blood ionized calcium levels fell below 1.0 mmol/L in 7 of 16 patients receiving R-568; five patients withdrew from study after developing symptoms of hypocalcemia, whereas three completed treatment after the dose of R-568 was reduced. CONCLUSIONS: The calcimimetic R-568 rapidly and markedly lowers plasma PTH levels in patients with secondary hyperparathyroidism caused by end-stage renal disease.
BACKGROUND & AIMS: Photodynamic therapy (PDT) is a technique for nonsurgical treatment of patients with dysplasia in Barrett's esophagus. The primary endpoint for PDT has been resolution of dysplasia. We studied the effect of PDT at the genetic level. METHODS: Archival material from 3 patients who had initial improvement in dysplasia after PDT but occurrence of high-grade dysplasia during follow-up was used. Biopsy specimens were analyzed for increased proliferation, aneuploidy, p53 protein overexpression, p53 mutations, and p16 promoter hypermethylation. RESULTS: Patients developed high-grade dysplasia 16, 28, and 37 months after PDT. In all cases, one or more genetic markers were positive after PDT treatment, whereas histology was downstaged consistently after therapy. Increasing genetic abnormalities were noted by the end of follow-up. CONCLUSIONS: Genetic abnormalities may persist after PDT despite phenotypical improvement of dysplasia. These patients may progress to high-grade dysplasia or develop adenocarcinoma. Histologic improvement in dysplasia is an inadequate endpoint for PDT in patients with Barrett's esophagus.
Isovaleric acidemia (IVA) is a recessive disorder caused by a deficiency of isovaleryl-CoA dehydrogenase (IVD). We have reported elsewhere nine point mutations in the IVD gene in fibroblasts of patients with IVA, which lead to abnormalities in IVD protein processing and activity. In this report, we describe eight IVD gene mutations identified in seven IVA patients that result in abnormal splicing of IVD RNA. Four mutations in the coding region lead to aberrantly spliced mRNA species in patient fibroblasts. Three of these are amino acid altering point mutations, whereas one is a single-base insertion that leads to a shift in the reading frame of the mRNA. Two of the coding mutations strengthen pre-existing cryptic splice acceptors adjacent to the natural splice junctions and apparently interfere with exon recognition, resulting in exon skipping. This mechanism for missplicing has not been reported elsewhere. Four other mutations alter either the conserved gt or ag dinucleotide splice sites in the IVD gene. Exon skipping and cryptic splicing were confirmed by transfection of these mutations into a Cos-7 cell line model splicing system. Several of the mutations were predicted by individual information analysis to inactivate or significantly weaken adjacent donor or acceptor sites. The high frequency of splicing mutations identified in these patients is unusual, as is the finding of missplicing associated with missense mutations in exons. These results may lead to a better understanding of the phenotypic complexity of IVA, as well as provide insight into those factors important in defining intron/exon boundaries in vivo.
The catalytic activities of Ret tyrosine kinases as the products of oncogene RET with multiple endocrine neoplasia type 2A (Ret-MEN2A) or 2B (Ret-MEN2B) mutations and the hybrid gene from c-RET and RFP (Rfp-Ret) were higher than those of c-Ret. We demonstrated that ultraviolet light (UV) irradiation induced activation of c-Ret and superactivation of genetically mutated, and thereby constitutively activated, Ret-MEN2A, Ret-MEN2B, and Rfp-Ret. We found that small proportions of c-Ret and Ret-MEN2B and a large proportion of MEN2A were dimerized due to disulfide bonds and that high kinase activity resided in these fractions. The UV-induced activation of c-Ret and superactivation of Ret-MEN2A and Ret-MEN2B were then shown to be closely associated with promotion of the disulfide bond-mediated dimerization of the Ret proteins. Furthermore, we showed that a large proportion of Rfp-Ret was dimerized or polymerized and that almost all kinase activities resided in the highly polymerized but not dimerized fraction. The UV-induced superactivation of Rfp-Ret was also found to be closely associated with promotion of polymerization but not with dimerization of Rfp-Ret. Further experiments revealed that UV induced intracellular dimerization and activation of the extracellular domain-deleted mutant Ret (Ret-PTC-1). Most importantly, the levels of basal kinase activity and dimerization of Ret-TPC-1-C376A, in which cysteine 376 in the tyrosine kinase domain of Ret-TPC-1 was replaced with alanine, were low and were not increased by UV irradiation. These results suggest that the cysteine at this position works as the primary target of dimerization of Ret proteins inside the cell for both the maintenance of the basal kinase activity and its promotion by UV, possibly in co-operation with the cysteine(s) in the extracellular domain of Ret-MEN2A and Rfp-Ret, which is the target of dimerization and polymerization outside the cell. The potential biological significance of the UV-mediated superactivation of mutant Ret through the newly proposed mechanism in oncogenesis is discussed.
The c-RET proto-oncogene encodes a receptor-type tyrosine kinase, and its mutations in the germ line are responsible for the inheritance of multiple endocrine neoplasia type 2A (MEN2A) and 2B (MEN2B). Ret kinases are constitutively activated as a result of MEN2A mutations (Ret-MEN2A) or MEN2B mutations (Ret-MEN2B). Here we demonstrate that UV light (UV) irradiation induces superactivation of the constitutively activated Ret-MEN2A and Ret-MEN2B as well as activation of c-Ret. Before UV irradiation, small percentages of c-Ret (3-4%) and Ret-MEN2B (1-2%) and large percentages of Ret-MEN2A (30-40%) were dimerized through disulfide bonds. These dimerized Ret proteins were preferentially autophosphorylated, suggesting a close relation between up-regulated kinase activity and disulfide bond-mediated dimerization of Ret proteins. We found that UV irradiation promotes the disulfide bond-mediated dimerization of the Ret proteins, in close association with activation and superactivation of Ret kinases. UV irradiation also induced dimerization and activation of the extracellular domain-deleted mutant Ret (Ret-PTC-1). Interestingly, the levels of basic kinase activity and dimerization of Ret-PTC-1-C376A, in which cysteine 376 in the tyrosine kinase domain of Ret-PTC-1 was replaced by alanine, were low and were not increased by UV irradiation. These results suggest that Ret-PTC-1 cysteine 376 is one of possibly multiple critical target amino acids of UV for Ret kinase activation. Overexpression of Cu/Zn superoxide dismutase in cells as a result of gene transfection prevented both the UV-mediated promotion of dimerization and the superactivation of Ret-MEN2A kinase. These results suggest that the UV-induced free radicals in cells attack intracellular domains of Ret to dimerize the kinase proteins for superactivation.
An attractive experimental method to elucidate the role of growth factors and cytokines in cutaneous wound healing would be to overexpress or "knock out" a molecule using a gene delivery vector and observe the impact on the wound repair process. As a first step toward developing an adenoviral gene delivery procedure to study wound repair, the authors injected beta-galactosidase (beta-gal) adenoviruses either subcutaneously or intradermally into the dorsal skin of 10-day-old postnatal Sprague-Dawley rats. Histological analysis and beta-gal staining were used to determine the expression and localization of the transferred gene. Beta-gal expression was observed as early as day 1 and up to day 7 postintradermal injection and day 9 postsubcutaneous injection, with no obvious inflammatory reaction detected at the injection sites. Furthermore, as expected, greater beta-gal expression was observed in the dermis of intradermally injected rats compared with the dermis of subcutaneously injected rats. Next, the authors sought to determine whether cutaneous wounds would heal before dissipation of the transferred gene. They created incisional and excisional wounds on the backs of similar-age rats. They found that incisional wounds closed by day 5 postwounding, whereas excisional wounds closed by day 14 postwounding. Their study demonstrated that an adenoviral vector delivered a gene efficiently into newborn rat skin and maintained the gene expression for at least as long as it would take for an incisional wound to heal. The combined use of newborn rat wound models and an adenoviral vector may provide a useful in vivo system to define the biological roles of growth factors and cytokines involved in the wound repair process. These discoveries may lead to the development of gene therapy approaches for abnormal wound healing.
OBJECTIVE: Activated neutrophils play a critical role in stress-induced gastric mucosal injury. We investigated the effect of ranitidine, an H2-receptor antagonist, on neutrophil activation in vitro and in rats with stress-induced gastric mucosal injury. DESIGN: Prospective, randomized, blinded, controlled study. SETTING: Research laboratory at a university medical center. INTERVENTIONS: Effects of ranitidine on neutrophil elastase release, production of O2-, intracellular calcium concentration and expression of adhesion molecules CD11b and CD18 were examined in human neutrophils in vitro. The effect of ranitidine (30 mg/kg iv) on the development of gastric mucosal injury, neutrophil accumulation, and lipid peroxidation was investigated in male Wistar rats subjected to water-immersion restraint stress. MEASUREMENTS AND MAIN RESULTS: Ranitidine inhibited the release of neutrophil elastase as well as the production of O2-, the increase in the concentrations of intracellular calcium, a second messenger of neutrophil activation, and increases in CD11b and CD18 expression, in activated neutrophils. Ranitidine did not affect the expression of E-selectin on endothelial cells in vitro. Ranitidine significantly inhibited gastric accumulation of neutrophils and gastric mucosal lipid peroxidation in rats subjected to stress. Although oral administration of acid reversed the preventive effect of pirenzepine, an anti-cholinergic drug that inhibits gastric acid secretion, it did not affect the preventive effect of ranitidine. Leukocytopenia produced effects similar to those of ranitidine in animals subjected to stress. CONCLUSIONS: Inhibition of neutrophil activation and gastric acid secretion by ranitidine might contribute to reduce stress-induced gastric mucosal injury.
The remarkable ability of the fetus to heal early gestation skin wounds without scarring remains poorly understood. Taking advantage of recent advances in signal transduction, the tyrosine phosphorylation patterns of fetal rat fibroblasts, representing the scarless cutaneous repair phenotype, and adult rat fibroblasts, representing scarforming phenotype, were examined whether there were inherent differences in cellular signaling. Specifically, correlation of the phosphorylation patterns with the expression levels of the signaling molecules that transmit information from the plasma membrane receptor to the nucleus was sought. By using three different cell lines of explanted fibroblasts from gestational day 13 fetal rat skin (n = 24) and 1-month-old postnatal adult rat skin (n = 3), immunoblotting was performed to compare tyrosine phosphorylation patterns. The results revealed five major protein bands of interest in fetal rat fibroblasts, but not in the adult rat fibroblasts. These phosphorylated protein bands are of interest because of their possible role in wound repair and may have the potential to regulate cellular responses to the extracellular matrix and their secondary signaling molecules. It was hypothesized that these bands represented receptor tyrosine kinases, epidermal growth factor receptor, and discoidin domain receptor 1, and their downstream adaptor protein Shc that binds receptor tyrosine kinases to transduce signals intracellularly. Furthermore, elevated expression of platelet-derived growth factor receptor-beta in adult compared with fetal fibroblasts was demonstrated, suggesting that decreased expression of certain growth factors may also be important for the scarless phenomenon to occur.
Keloids represent a dysregulated response to cutaneous wounding that results in disfiguring scars. Unique to humans, keloids are characterized by an accumulation of extracellular matrix components. The underlying molecular mechanisms of keloid pathogenesis, however, remain largely uncharacterized. Similarly, cellular signaling mechanisms, which may indicate inherent differences in the way keloid fibroblasts and normal human dermal fibroblasts interact with extracellular matrix or other cells, have not been investigated. As part of a fundamental assessment of cellular response to injury in keloid fibroblasts, phosphorylation studies were performed using three different keloid (n = 3) and normal human dermal (n = 3) fibroblast cell lines. These studies were undertaken to elucidate whether keloid and normal human dermal fibroblasts exhibit different tyrosine kinase activity. Initially, distinct tyrosine phosphorylation patterns of keloid and normal human dermal fibroblasts were demonstrated. Next, the phosphorylation patterns were correlated with known molecules that may be important to keloid pathogenesis. On the basis of molecular weight, it was hypothesized that the highly phosphorylated bands seen in keloid fibroblasts represented epidermal growth factor receptor (EGFR); discoidin domain receptor 1 (DDR1); and Shc, an adaptor protein known to bind many tyrosine kinases, including EGFR and DDR1. Individual immunoblotting using EGFR, DDR1, and Shc antibodies revealed greater expression in keloid fibroblasts compared with normal human dermal fibroblasts. These data substantiate for the first time the finding of greater phosphorylation by the above-mentioned molecules, which may be important in keloid pathogenesis.
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Using a custom galvanotaxis chamber and time-lapse digital video microscopy, we report the novel observation that cultured chondrocytes exhibit cathodal migration when subjected to applied direct current (DC) electric fields as low as 0.8 V/cm. The response was dose-dependent for field strengths greater than 4 V/cm. Cell migration appeared to be an active process with extension of cytoplasmic processes in the direction of movement. In some cells, field application for greater than an hour induced elongation of initially round cells accompanied by perpendicular alignment of the long axis with respect to the applied field. Antagonists of the inositol phospholipid pathway, U-73122 and neomycin, were able to inhibit cathodal migration. Cell migration toward the cathode did not require the presence of serum during field application. However, the directed velocity was nearly threefold greater in studies performed with serum. Studies performed at physiologic temperatures (approximately 37 degrees C) revealed a twofold enhancement in migration speed compared to similar studies at room temperature (approximately 25 degrees C). Findings from the present study may help to elucidate basic mechanisms that mediate chondrocyte migration and substrate attachment. Since chondrocyte migration has been implicated in cartilage healing, the ability to direct chondrocyte movement has the potential to impact strategies for addressing cartilage healing/repair and for development of cartilage substitutes.
C-1027, the most potent member of the enediyne antitumor antibiotic family, is produced by Streptomyces globisporus C-1027 and consists of an apoprotein (encoded by the cagA gene) and a nonpeptidic chromophore. The C-1027 chromophore could be viewed as being derived biosynthetically from a benzoxazolinate, a deoxyamino hexose, a beta-amino acid, and an enediyne core. By adopting a strategy for cloning of the C-1027 biosynthesis gene cluster by mapping a putative dNDP-glucose 4,6-dehydratase (NGDH) gene to cagA, we have localized 75 kb of contiguous DNA from S. globisporus. DNA sequence analysis of two regions of the cloned gene cluster revealed two genes, sgcA and sgcB, that encode an NGDH enzyme and a transmembrane efflux protein, respectively, and confirmed that the cagA gene resides approximately 14 kb upstream of the sgcAB locus. The involvement of the cloned gene cluster in C-1027 biosynthesis was demonstrated by disrupting the sgcA gene to generate C-1027-nonproducing mutants and by complementing the sgcA mutants in vivo to restore C-1027 production. These results represent the first cloning of a gene cluster for enediyne antitumor antibiotic biosynthesis and provide a starting point for future genetic and biochemical investigations of C-1027 biosynthesis.
New outbreaks of human immunodeficiency virus type 1 (HIV-1) among injecting drug users (IDUs) are spreading in China along heroin trafficking routes. Recently, two separate HIV-1 epidemics among IDUs were reported in Guangxi, Southern China, where partial sequencing of the env gene showed subtype C and circulating recombinant form (CRF) AE. We evaluated five virtually full-length HIV-1 genome sequences from IDUs in Guangxi to determine the genetic diversity and the presence of intersubtype recombinants. Sequence analysis showed two geographically separated, highly homogeneous HIV-1 strains. B/C intersubtype recombinants were found in three IDUs from Baise City, in a mountainous region near the Yunnan-Guangxi border. These were mostly subtype C, with portions of the capsid and reverse transcriptase (RT) genes from subtype B. The subtype B portion of the capsid was located in the N-terminal domain, which has been shown to influence virus core maturation, virus infectivity, and binding to cyclophilin A, whereas the subtype B portion of RT was located in the palm subdomain, which is the active site of the enzyme. These BC recombinants differed from a BC recombinant found in Xinjiang Province in northwestern China. CRF AE strains were found in IDUs from Nanning, the capital of Guangxi, and in IDUs from Pingxiang City near the China-Vietnam border. The AE and BC recombinants were both remarkable for their low interpatient diversity, less than 1% for the full genome. Rapid spread of HIV-1 among IDUs may foster the emergence of highly homogeneous strains, including novel recombinants in regions with multiple subtypes.
PURPOSE: To evaluate a low-dose, nonenhanced helical computed tomographic (CT) protocol in the detection of ureteric stones and measure the associated effective dose equivalent (H(E)) of radiation. MATERIALS AND METHODS: Sixty patients suspected of having renal colic and referred by emergency department physicians underwent nonenhanced helical CT with 7-mm collimation and a 2:1 pitch and then conventional intravenous urography (IVU). The two studies were prospectively and independently interpreted. The diagnostic accuracy of CT for ureteric stone detection was determined by comparing the scans with the IVU images and with a combination of clinical, surgical, and other imaging findings. The radiation risk from typical CT and IVU examinations (five images) was measured in terms of H(E) and compared with the estimated risk from two previously reported CT protocols. RESULTS: CT correctly depicted 36 of 37 ureteric stones, and one false-positive case was recorded, for a sensitivity of 97%, specificity of 96%, and accuracy of 97%. The H(E) for our CT protocol was determined to be 2.8 mSv, which is about double that for IVU and about 75% and 50% of that for two previously reported CT protocols. CONCLUSION: Our low-dose CT protocol is superior to IVU and clinically adequate for diagnosis of renal colic.
Hyperosmolarity is a stress factor that has been shown to cause an increase in the transcription of the Na(+)-dependent myo-inositol cotransporter (SMIT). However, regulation of the reversion of SMIT mRNA levels and transporter activity following removal of hyperosmotic stress is less understood. Previously we have shown that postinduction normalization of SMIT mRNA levels and myo-inositol accumulation following removal of hyperosmotic stress is inhibited by actinomycin D and cycloheximide, suggesting that normalization requires RNA transcription and protein synthesis. We now demonstrate that removal of hyperosmotic stress causes an activation of the transcription factor NF-kappaB in renal and endothelial cells. Inhibiting NF-kappaB activation with pyrrolidine dithiocarbamate (PD) blocks the normalization of SMIT mRNA levels and myo-inositol accumulation on removal of the cells from hyperosmotic medium. These studies demonstrate that the downregulation of the myo-inositol transporter following reversal of hyperosmotic induction is regulated via the activation of NF-kappaB.
To better understand the molecular mechanisms for hyperglycemia-induced proatherogenic changes in endothelial cells, the effect of high glucose on activation of members of the mitogen-activated protein kinase (MAPK) family, including c-Jun NH(2)-terminal kinase (JNK), extracellular signal-regulated kinase (ERK)-1, -2, and -5, and p38 kinase, was examined in bovine pulmonary artery endothelial cells (PAEC). Glucose, fructose, and raffinose induced a concentration-dependent decrease in PAEC growth. Addition of 25 mM glucose, fructose, or raffinose to normal growth medium stimulated an approximately twofold increase in JNK1 activity that was maximal after 24 h, whereas only glucose markedly increased ERK5 activity. Neither ERK1/2 nor p38 kinase activity was increased by glucose, fructose, or raffinose. The antioxidant N-acetylcysteine partially abrogated the glucose-induced increase in ERK5 activity but had no effect on the increase in JNK1 activity. In contrast, azaserine, which prevents increased flux through the hexosamine pathway, decreased glucose-induced JNK1 activity but had no effect on fructose- or raffinose-induced JNK1 activity. Consistent with this finding, glucosamine stimulated a 2.4-fold increase in JNK1 activity and reproduced the inhibitory effect of glucose on PAEC growth. In summary, glucose activates different members of the MAPK family in PAEC via distinct mechanisms. Moreover, the correlation between the ability of different sugars to activate JNK1 and inhibit cell growth suggests that activation of this signaling pathway may contribute to the growth inhibitory effect of glucose in endothelial cells.
Apoptosis of mesothelial cells has been demonstrated in vitro but not in vivo. To identify apoptotic pleural cells as mesothelial, we used cytokeratin as a marker and found a striking spheroid, aggregated appearance of cytokeratin in apparently apoptotic mesothelial cells. In in vitro studies, we found that the aggregated cytokeratin pattern correlated with apoptosis in primary mesothelial cells from mice, rabbits, and humans and was not seen with necrosis. In in vivo studies in mice, we then used this cytokeratin pattern to identify and quantitate apoptotic mesothelial cells. Apoptotic mesothelial cells were best harvested by pleural lavage, indicating that they were loosely adherent or nonadherent. Instillation of RPMI 1640 medium or wollastonite for 24 h induced apoptosis in 0.1 +/- 0. 1 (SE) and 1.0 +/- 0.7%, respectively, of all mesothelial cells recovered, whereas instillation of known apoptotic stimuli, crocidolite asbestos (25 microg) for 24 h or actinomycin D plus murine tumor necrosis factor-alpha for 12 h, induced apoptosis in 5. 1 +/- 0.5 and 22.4 +/- 4.5%, respectively (significantly greater than in control experiments, P < 0.05). By analysis of cytokeratin staining, mesothelial cell apoptosis has been confirmed in vivo.